1. Field of the Invention
The present invention relates to a high-aseismic RC (reinforced concrete) pier.
2. Description of the Related Art
There are conventionally known, for example, PC (prestressed concrete) piers as high-aseismic piers. The PC piers are subjected to prestresses to increase strength and rigidity of the piers, thereby reducing a residual plastic deformation after strong earthquakes. However, the PC piers have disadvantages in that the prestresses increase permanent stresses in the concrete, thereby making a maximum strength-relevant deformation, caused when the concrete is collapsed, less than that of usual RC piers, with decrease of the deformation characteristic.
On the other hand, there are known RC members mixedly using reinforcing bars of a variety of strengths. The object of these RC members resides in that using reinforcing bars of different yield strengths and yielding their reinforcing bars in turn provides secondary rigidity to the load-deformation relationship. However, when the deformation is large, all the reinforcing bars yield, thereby disabling an elastic restoring force to be obtained, which makes it difficult to decrease the residual plastic deformation.
A general aseismic design is carried out in two steps; the first step is to carry out a strength design for an earthquake of level I which is relatively high in frequency, and the second step is to carry out a horizontal strength check of evaluating the deformation characteristic, including a plastic zone of the member, for an earthquake of level to which is low in frequency, but very strong. Also, the above aseismic design requests that the residual deformation ranges within the specified ratio (1/100 in Japan) of the height of the pier in order to make repairs in its relatively early steps after the large earthquake. That is, the piers having a large earthquake-resistance are ones having both of high strength for the earthquake of level I and of large toughness and a small residual deformation for the earthquake of level II. In particular, however, the requirement items of the large toughness and the small residual deformation for the earthquake of level II are contradictory to each other, which makes it difficult for the conventional RC piers to unite them.
It is therefore an object of the invention to provide a pier which is capable of advantageously solving the above-mentioned problems.
The present invention provides a reinforcing concrete pier comprising a concrete member, and structural main reinforcing bars embedded in the concrete member so as to extend along an axial direction of the concrete member, characterized in that a high-strength core member, which is higher in strength than the structural main reinforcing bars, is embedded in the concrete member inside the structural main reinforcing bars so as to extend along the axial direction; one end portion of the core member is fixed to the concrete member at a base portion of the pier, and the other end portion of the core member is fixed to the concrete member at an intermediate portion of the pier; and the core member has an unbounded region in which the core member is not bonded to the concrete member between the one end portion and the other end portion.
According to the reinforced concrete pier of the invention, the core member is made of material higher in strength than the structural main reinforcing bar in such a manner that the core member takes an elastic behavior when the pier is deformed largely, and arranged inside the structural main reinforcing bars, and the unbonded region is provided between the base portion and the intermediate portion, thereby causing the core member to be equalized in stress all over the total length of the core member. The high-strength core member surely raises secondary rigidity in a plastic region of the deformation-restoring force of the pier, and increases the final deformation characteristic corresponding to the yield strength.
Accordingly, according to the reinforced concrete pier of the invention, the secondary rigidity in the plastic region of the deformation-restoring force of the pier is improved, and the deformation characteristic increases up to the deformation corresponding to the yield strength, thereby resulting in reasonable (economical) improvement of the aseismic design for the earthquake of level II, and simultaneously the yield strength is increased, thereby resulting in improvement of the aseismic design for the earthquake of level I. And also, the high-strength core member is not subjected to prestresses, thereby making the construction work much easier compared to the PC pier.
Moreover, in this embodiment, it is preferred that at least one end portion of the core member has an axial direction-wise gap, a magnitude of which sets a deformation amount of the pier at which the core member starts resisting against a tensile force.
According to this construction, the deformation amount of the pier in which the core member stars resisting against the tensile force and then the secondary rigidity occurs can be set in a desired manner by adjusting a magnitude of the axial direction-wise gap, thereby enabling the core member to act on a deformed region of the pier in which the pier is deformed largely, which makes the final deformation corresponding to the yield strength large.